Various types of off-road or construction vehicles are used to perform excavation functions such as leveling, digging, material handling, trenching, plowing, etc. These operations are typically accomplished with the use of a hydraulically operated bucket, backhoe or other implement. These implements include a plurality of linkages translationally supported and rotationally supported, and are moved relative to the supports by hydraulic cylinders or motors. As a result of the type of work excavators are used to perform (i.e. job site excavation) these excavators are often required to travel on roads between job sites. Accordingly, it is important that the vehicle travel at reasonably high speeds. However, due to the suspension, or lack thereof, and implements supported on the vehicle, vehicle bouncing, pitching or oscillation occurs at speeds satisfactory for road travel.
In an attempt to improve roadability, various systems have been developed for interacting with the implements and their associated linkages and hydraulics to control bouncing and oscillation of excavation vehicles while operating at road speeds. One such system includes circuitry for lifting and tilting an implement combined with a shock absorbing mechanism. This system permits relative movement between the implement and the vehicle to reduce pitching of the vehicle during road travel. To inhibit inadvertent vertical displacement of the implement, the shock absorbing mechanism is responsive to lifting action of the implement. The shock absorbing mechanism is responsive to hydraulic conditions indicative of imminent tilting movement of the implement thereby eliminating inadvertent vertical displacement of the implement.
Other systems for improving the performance of excavators have included accumulators which are connected and disconnected to the hydraulic system depending upon the speed of the vehicle. More specifically, the accumulators are connected to the hydraulic system when the excavator is at speeds indicative of a driving speed and disconnected at speeds indicative of a loading or dumping speed.
These systems may have provided improvements in roadability, but it would be desirable to provide an improved system for using the implements of excavation vehicles to improve roadability. Accordingly, the present invention provides a control system which controls the pressure in the lift cylinders of the implement(s) associated with an excavation vehicle based upon the acceleration of the vehicle.